There was a trail of what are commonly known as sugar ants (small, brown, hyperactive) in my kitchen. Three of them walked onto an ice tray placed in their path.

They only walked a short distance on the ice before being immobilized by cold. I put the tray in the freezer beside a very shallow dish of water. When the water in the dish had frozen (about a half hour later) I removed the tray/ants and let them passively drop onto a warm dry surface. After 2-3 minutes they revived, walked in circles a few times, then headed off to forage (they were released outdoors).

There is anecdotal evidence of ants' tolerance of cold but I was a little surprised by this. Do we know the extent of their tolerance of cold?

I guess it would vary with size and conditions. But an obvious question is whether, having survived freezing at (let's say) 22F, they could survive lower temperatures and/or longer periods of cold if properly handled? There may be cell structures that are sensitive to freezing because they break or change shape but it's already amazing to me that ordinary freezing does not distort water-bound structures in a lethal way.

1 Answer
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Acclimatization increases cold resistance of ants [1]. They have a strong adaptability to different environments [2].

When it comes to the red imported fire ant (Solenopsis invicta) here are some numbers (from [2]):

When the exposure time was 0.5 h, the survival rate of workers was 15.3% at -14°C. At the exposure time of 1, 2 and 4 h, the entire lethal temperatures for S. invicta were -13°C, -9°C and -9°C, respectively. When the exposure temperature was -10°C, all workers died within 240 min; while at -11°C, it took only 120 min.